What is the output waveform of 120V 300W UPS like? Square or Sinewave?

Thread Starter

Rahulk70

Joined Dec 16, 2016
451
Hi everyone,

I have an APC BK500MC 120V-300W (2002 model with only seriel port and two backup outlets and one surge output port)UPS with me. Just wanted to know if these normal UPS produce pure sinewave or are they those square wave inverters? Got a fan motor 208~230V 100W 1.2A from an A/C today, stepped it up with a 110V to 220V 100VA stepup transformer tried to test if its working and it did spin the fan but there was kinda loud hum when I ran it. But that noise isn't there when I tried to run it on a 220V outlet. So, is it because of the square wave from the UPS/Inverter? (Note: I don't have an oscilloscope with me to test its output waveform)
Thanks
 

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Reloadron

Joined Jan 15, 2015
5,120
I see two flavors which I have always refereed to as a MSW (Modified Sine Wave) and a PSW (Pure Sine Wave. Both are popular with inverters and the latter PSW is the more expensive of the two.

Pure Sine Wave Vs. Modified Sine Wave is a basic read on the subject.

Anyone who remembers the early automotive AM car radios remembers the vacuum tubes in them and the "warm up" time. The B+ voltage for the vacuum tubes or Valves for my friends across the pond was generated using a vibrator (mechanical reed vibrator)which drove a transformer with a sort of ugly square wave and the transformer produced a high voltage which was rectified by a HV Rectifier tube. The first transistorized car radios I recall were the early 60s.

Oh yeah, of late the stepped sine wave has become popular. I forgot about that flavor. A stepped sine wave looks pretty much like the name implies.

The consideration is what the sine wave will be powering. Obviously an incandescent light bulb won't care. I understand newer home computer power supplies and other sensitive electronics can be fussy.

Ron
 
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The Electrician

Joined Oct 9, 2007
2,767
I don't have access to an oscilloscope at the moment and cannot find the information you require online or via the manual.

"Stepped approximation to a sinewave" is all I can find.

I find it strange you ask how many steps in a quarter cycle?
The number of steps in a quarter cycle is the minimum description of the complete waveform (the negative half cycle should be a mirror image of the positive half cycle), not counting zero volts. So-called "stepped" approximations to a sine wave can vary from not so good, to quite good.

For example, here's an image comparing a pure sine wave (black) with a "stepped" approximation consisting of only 1 voltage step (blue) and 3 steps (red): https://www.bing.com/images/search?view=detailV2&ccid=2cc9xR6k&id=2EA4B3CDEB93B7CDB6D9FFEBB028AE3608976F46&thid=OIP.2cc9xR6kp6qERsVPn6hTbwEsD2&q=stepped+sine+wave&simid=608028256564677040&selectedIndex=1&qpvt=stepped+sine+wave&ajaxhist=0

Here we have 2 steps: https://www.bing.com/images/search?view=detailV2&ccid=ykPhwIOL&id=DC299787E68E0779AB126F6AB2AB53D6A162EC04&thid=OIP.ykPhwIOLRQqSeeM67soFSAEsC2&q=stepped+sine+wave&simid=608022900748455374&selectedIndex=52&ajaxhist=0

Here we have 4 steps: https://www.bing.com/images/search?view=detailV2&ccid=At4tJnvs&id=DD88264CEC8E5F06D461C6D48CDDDB84445399BC&thid=OIP.At4tJnvs-4l3XyZdr0rCqQEsBi&q=stepped+sine+wave&simid=608052471591014030&selectedIndex=15&qpvt=stepped+sine+wave&ajaxhist=0

And finally, 8 steps: https://www.bing.com/images/search?view=detailV2&ccid=YUNQGD1/&id=FFCBB9860BB23910615020D4FB1E5F8FCBD5450F&thid=OIP.YUNQGD1_cPXhzMVC9P2zJgEsDI&q=stepped+sine+wave&simid=608001614888701798&selectedIndex=12&qpvt=stepped+sine+wave&ajaxhist=0
 

ErnieM

Joined Apr 24, 2011
8,019
According to APC the output type is a "stepped approximation to a sine wave."

Such waveforms have high frequency components that can saturate transformers and or motors.
 
Your time to explain is appreciated, I do know the ins and outs, but still found it strange you ask about quarter cycles rather than half or even full.

Here we have 4 steps: https://www.bing.com/images/search?...tedIndex=15&qpvt=stepped+sine+wave&ajaxhist=0

Something wrong here?
As I said, "The number of steps in a quarter cycle is the minimum description of the complete waveform". Any more is redundant.

The 2nd, 3rd and 4th quarter cycles are the same as the first quarter cycle, possibly inverted or mirror image. Counting the number of steps in the full cycle doesn't add any information. The hardware only has to generate the number of voltage steps in the first quarter cycle, with polarity and order reversed for the rest.

In hardware that generates a sine wave from a table of values it's only necessary to have the values for the first quarter cycle. Having a table for the complete cycle would be 4 times longer than necessary, just duplicating the values in the first quarter cycle with different order or sign.
 

Reloadron

Joined Jan 15, 2015
5,120
For the curious at heart AN-263 Sine Wave Generation Techniques by Texas Instruments is really a pretty good read. They cover sine approximation quite well including the common methods of:
8 Approximation Methods ................................................................................................... 10 9
Sine Approximation—Breakpoint Shaper ............................................................................ 11 10
Sine Approximation—Logarithmic Shaping ......................................................................... 12 11
Sine Approximation—Voltage Controlled Sine Oscillator .................................................... 13 12
Sine Approximation—Digital Methods ................................................................................. 14

Sine approximation using digital methods is interesting in the the D to A bit count defines how good the sine wave really is. The circuits are easy to understand.

Ron
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
451
Thanks for the replies everyone.So, basically the APC UPS I've has a stepped sine wave I understand and pure sine wave is available only in really expensive inverters/UPS.In the later case the inductive or motor would not produce the hum. Right? Some of the members have given replies deeper into the subject giving a better understanding. :)
 

Reloadron

Joined Jan 15, 2015
5,120
This is your unit.

Technical Specifications:
  • Max Configurable Power (Watts)
    300Watts / 500VA
  • Nominal Output Voltage
    120V
  • Output Frequency (sync to mains)
    50/60Hz +/- 3 Hz
  • Topology
    Standby
  • Waveform type
    Stepped approximation to a sinewave
  • Maximum Output Current
    10
  • Output Connections
    (3) NEMA 5-15R (Battery Backup)
    (3) NEMA 5-15R (selector_surgetitle)
  • Transfer Time
    8ms typical : 12ms maximum
That about covers it. True sine wave output units can get expensive. This thread served to remind me of the changes in UPS units so thanks. All I still have is some old APC 1500 units around here. During a power failure they only need to run about 10 seconds or less before the automatic generator is online. I was not aware that most UPS units no longer have the MSW output and have gone to a uC created stepped sine wave.

Ron
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
451
This is your unit.

Technical Specifications:
  • Max Configurable Power (Watts)
    300Watts / 500VA
  • Nominal Output Voltage
    120V
  • Output Frequency (sync to mains)
    50/60Hz +/- 3 Hz
  • Topology
    Standby
  • Waveform type
    Stepped approximation to a sinewave
  • Maximum Output Current
    10
  • Output Connections
    (3) NEMA 5-15R (Battery Backup)
    (3) NEMA 5-15R (selector_surgetitle)
  • Transfer Time
    8ms typical : 12ms maximum
That about covers it. True sine wave output units can get expensive. This thread served to remind me of the changes in UPS units so thanks. All I still have is some old APC 1500 units around here. During a power failure they only need to run about 10 seconds or less before the automatic generator is online. I was not aware that most UPS units no longer have the MSW output and have gone to a uC created stepped sine wave.

Ron
Thank you very much Ron. That was very detailed answer and the specs which I've been looking for. I searched online for the user manual but its for the newer model of this variant APC 500 CS if I remember is only available. I had another APC 5000 that was given to me long back was lying in the garage for a while, its big waste of space and I don't have much use for it now. Thinking of throwing it away. APC is a pretty reliable brand among varoius UPS I've used.
 

ian field

Joined Oct 27, 2012
6,539
I would say they will be sine wave, or stepped sine using a microcontroller.
Depends how much the TS paid for it. Cheap low power units from discount stores are just a square wave, pay a bit more and you might get a stepped square wave that will not upset so many appliances. Pay top dollar and you might get something pretty close to a sinewave.
 
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